Parkinson's disease (also known as Parkinson disease, Parkinson's, idiopathic parkinsonism, primary parkinsonism, PD, or paralysis agitans) is a degenerative disorder of the central nervous system. It results from the death of dopamine-containing cells in the substantia nigra, a region of the midbrain; the cause of cell-death is unknown. Early in the course of the disease, the most obvious symptoms are movement- and balance-related, including shaking, rigidity, falls, freezing of gait, slowness of movement and difficulty with walking and gait. The main motor symptoms are collectively called parkinsonism, or a “parkinsonian syndrome”. The pathology of the disease is characterized by the accumulation of a protein called alpha-synuclein into inclusions called Lewy bodies in neurons, and from insufficient formation and activity of dopamine produced in certain neurons of parts of the midbrain.